Melt spun cellulose based fibers

ABSTRACT

According to an example aspect of the present invention, there is provided a melt spinning method of cellulose based fibers with controlled molar masses and different side lengths, and continuous melt spun cellulose fibers thereof.

FIELD

The present invention relates to melt spun cellulose based fibers, especially molar mass controlled cellulose (MMCC) esters and their use for production of man-made continuous fibers by a melt spinning process.

BACKGROUND

Biopolymers and bioplastics market has a very large growth potential in the future. According to estimation, bio-based polymer production capacity is expected to grow from 1.7 Mton in 2014 to 7.8 Mton in 2019 (5-times). Several well-known companies have announced that they are interested in replacing oil-based polymers with 100% renewable materials. Melt spinning is one of the most economical and convenient methods for manufacturing continuous fibers in large quantities for the textile industry.

At the moment major part of the artificial fibers that are used for apparel and home furnishing are made from fossil oil. Burning products made from fossil oil increases the CO₂ level of the atmosphere and accelerates the effect of the climate change. Thermoplastic material used for the production of the artificial fibers has to have suitable properties from the processing perspective.

Only a few results of cellulose based melt spinning fibers, which have been prepared using cellulose acetate butyrate (CAB), have been earlier reported. (Chen et al. 2010; Hooshmand et al. 2014b, a; Wang et al. 2018) However, plasticizers (e.g. triethyl citrate) are required for all these reported short chain cellulose derivatives.

WO 2016/193542 A1 discloses general methods for improving the reactivity and processability of cellulose providing a starting point for hydrolyzed and reactive molar mass controlled cellulose having thermoplastic properties.

JP 2005/248354 A discloses a method for producing a cellulose fatty acid ester fiber having excellent mechanical properties, particularly strength and elastic modulus, and excellent productivity. It also describes melt spinning method for preparing continuous cellulose based fibers. However, controlling of molar mass and molar mass distribution of the dissolving pulp raw material by means of hydrolysis is not disclosed. In addition, the document discloses the use of 5 to 25% by weight of polyhydric alcohol plasticizer and high melt spinning temperatures between 260 and 340° C.

There is a need for means to modify cellulose fibers in order to have different thermoplastic properties for providing greater use of cellulose-based materials in melt spun fiber production, preferably without additional plasticizers, and by using low melt spinning temperatures.

SUMMARY OF THE INVENTION

The invention is defined by the features of the independent claims. Some specific embodiments are defined in the dependent claims.

According to an aspect of the present invention, there is provided a melt spinning method for preparing continuous cellulose based fibers.

According to another aspect of the present invention, there is provided a melt spinning method for preparing continuous cellulose based fibers from a fully bio-based molar mass controlled cellulose esters, and melt spun fibers thereof having moderate mechanical properties for various end-uses, such as purposes of the textiles industry.

These and other aspects, together with the advantages thereof over known solutions are achieved by the present invention, as hereinafter described and claimed.

The melt spinning method according to the present invention is mainly characterized by what is stated in the characterizing part of claim 1.

The melt spun fiber according to the present invention is characterized in claim 10.

Considerable advantages are obtained by means of the invention. Melt spinning process is one of the most convenient methods for polymer fiber manufacturing at industrial scales for the textile industry. Melt spinning is a simple process, which offers many advantages compared to solvent or wet fiber spinning, such as no solvents is needed, there are no toxic by-products, and the production speed is high. Used MMCC grades are fully bio-based thermoplastic materials. Furthermore, the suitability of the MMCC in fiber production is herein demonstrated without the addition of plasticizer(s).

Next, the present technology will be described more closely with reference to certain embodiments.

EMBODIMENTS

The present technology provides melt spinning process of thermoplastic cellulose esters. The molar mass controlled cellulose esters with different side chain length were synthesized with different degrees of substitution (DS), and the suitability of these cellulose esters for fiber production was evaluated. To see the differences in thermal behaviors, capillary rheometer tests were conducted and according to these results, the best cellulose ester was chosen to bigger scale melt spinning tests.

FIG. 1 is a chart showing capillary rheometer test for a cellulose hexanate and cellulose octanates compared to a polypropylene reference.

FIG. 2 is an image showing melt spun A) cellulose hexanate fiber (DS 1.5) and B) cellulose octanate fiber (DS 1.5).

FIG. 3 is a SEM image of the A) cross-section and B) surface of the melt spun cellulose octanate fiber at 300×magnification. Scale bar=20 μm.

In the present invention several different grades of molar mass controlled cellulose (MMCC) with different side chain lengths (C6-C16) and degree of substitution (DS) were tested. According to one embodiment of the present invention it was found out that molar mass controlled cellulose octanate (MMCC C8) having degree of substitution of 1.4 provided one suitable starting point for the greater use of cellulose-based starting materials in melt spun fiber production.

According to one embodiment of the present invention, the present melt-spinning method includes preparing continuous cellulose based fibers, comprising at least the steps of:

-   -   preparing from a cellulose raw material a molar mass controlled         cellulose ester having side length between C2 and C18, total         degree of substitution from 0.7 to 3 and molar mass distribution         between 30 and 300 kDa,     -   carrying out melt spinning of the molar mass controlled         cellulose ester by using a melt spinning device, and     -   collecting the melt spun fibers.

According to one embodiment, the method comprises controlling (i.e. decreasing) the molar mass of a cellulose raw material via hydrolysis, excluding total hydrolysis, and by performing a long chain fatty acid modification, e.g. esterification or hydroxyalkylation for the molar mass controlled cellulose.

According to a further embodiment of the present invention, the hydrolysis is controlled so that the average molecular mass of the cellulose is reduced at least 60% but not more than 85% from the molecular mass of the starting raw material. It is preferred that the hydrolysis is controlled so that after the hydrolysis the average molecular mass of the cellulose is between 30 to 300 kDa, preferably between 40 to 200 kDa. It should be noted that the molar mass of the cellulose is indeed controlled, whereby the cellulose is not subjected to total hydrolysis.

According to one embodiment, the cellulose raw material is selected from native softwood pulp, native hardwood pulp, annual plant pulps such as bamboo pulp or straw pulp, softwood sulphite dissolving grade pulp, hardwood sulphite dissolving grade pulp, ozone treated hydrolyzed pulp or enzyme treated pulp.

According to a further embodiment, cellulose is hydrolyzed and thus activated by enzymatic treatment, ozone treatment, hydrogen peroxide treatment, alkaline treatment, or other chemical treatment, before performing a long chain fatty acid modification, such as an esterification or hydroxyalkylation.

The molar mass controlled cellulose ester usable in the present method may be prepared for example by homogenous esterification of the cellulose raw material. In this method, fatty acid chloride (C6, C8, C12 or C16, 3 or 4 equivalents to cellulose anhydroglucose unit; AGU) was added to the cellulose mixture using pyridine as catalyst. The reaction temperature was 80° C. and reaction time 16 hours. The product was precipitated with ethanol and washed with ethanol and acetone.

According to one embodiment of the present invention, the molar mass controlled cellulose ester preferably has a side length between C6 and C16, such as C8.

According to one embodiment of the present invention, the molar mass controlled cellulose ester preferably has a total degree of substitution between 0.9 and 2.0, such as 1.4.

According to one embodiment of the present invention, melt spinning is performed at a temperature between 120 and 150° C., more preferably between 125 and 140° C., by using a melt spinning device having single screw extruder, melt pump and multi strand filament die.

Thus, one suitable way to carry out the melt spinning step is to use a Fourne melt spinning machine (Fourne Polymertechnik GmbH, Germany) consisting of a 10 mm single screw extruder (rate 100 rpm), melt pump (rate 14 rpm) and multi strand filament die. In one example the spinneret with 8 holes (diameter of 0.7 mm) was used. Spinning was performed at 130° C. The material was dried at ambient vacuum over night before processing. The melt spun fibers were collected and oriented using a drawing speed range of 0-200 m/min with and without an avivage agent.

A fully bio-based continuous melt spun molar mass controlled cellulose fiber having good mechanical properties as the foregoing examples and figures show belongs also to the scope of the present invention.

Reference throughout this specification to one embodiment or an embodiment means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Where reference is made to a numerical value using a term such as, for example, about or substantially, the exact numerical value is also disclosed.

While the forgoing examples are illustrative of the principles of the present invention in one or more particular applications, it will be apparent to those of ordinary skill in the art that numerous modifications in form, usage and details of implementation can be made without the exercise of inventive faculty, and without departing from the principles and concepts of the invention. Accordingly, it is not intended that the invention be limited, except as by the claims set forth below.

The verbs “to comprise” and “to include” are used in this document as open limitations that neither exclude nor require the existence of also un-recited features. The features recited in depending claims are mutually freely combinable unless otherwise explicitly stated. Furthermore, it is to be understood that the use of “a” or “an”, that is, a singular form, throughout this document does not exclude a plurality.

INDUSTRIAL APPLICABILITY

Technical and hygienic nonwovens are the fastest growing textile materials, originating typically from fossil synthetic polymers. Novel thermoplastic cellulose fatty acid esters have polyolefin like properties and therefore the suitability of these cellulose esters for fiber production was herein evaluated. The present invention demonstrates melt spinning of textile fibers by using thermoplastic molar mass controlled cellulose. The melt spinning results indicate that the novel cellulose based fibers can provide a renewable and recyclable alternative for e.g. polypropylene in several technical and hygienic textile applications.

EXAMPLES Materials

The cellulose materials for esterification were commercial softwood dissolving grade pulp produced by Domsjö Fabriker AB (Sweden) and the pulp was ozone pretreated according to a method described by Willberg-Keyriläinen et al. (2016). Polypropylene (PP) was used as reference material and commercial Tallopol SLB (Bozzetto, Italy) was used as an avivage agent. All other reagents and solvents were purchased from Sigma-Aldrich (Helsinki, Finland) in the highest purity grade available and were used as received.

Preparation of Cellulose Esters

The homogenous esterification of the cellulose was conducted using the method presented by Willberg-Keyrilainen et al. (2016, 2017a). In this method, fatty acid chloride (C6, C8, C12 or C16, 3 or 4 equivalents to cellulose anhydroglucose unit; AGU) was added to the cellulose mixture using pyridine as catalyst. The reaction temperature was 80° C. and reaction time 16 hours. The product was precipitated with ethanol and washed with ethanol and acetone. Solid State Nuclear Magnetic Resonance (ssNMR) The cellulose esters were analyzed using the solid state ¹³C CP/MAS NMR spectroscopy (ssNMR) analyses were carried out using an Agilent 600 MHz NMR spectrometer (Agilent Technologies, USA). All ssNMR experiments were carried out at 22° C. using MAS rate of 10 kHz, 10 000 scans and 10 s recycle time.

Capillary Rheometer

Spinnability of prepared cellulose esters was first evaluated with Göttfert Rheograph 6000 capillary rheometer (Gottfert, Germany). The capillary rheometry was carried out by using a 1/30 mm die and a shear rate range from 30 s⁻¹ to 1000 s⁻¹. Tests were performed at 130° C. with 3 min preheating time. Apparent values were recorded and spinnability was assessed by hand. Prior to experimenting, the materials were dried in vacuum overnight.

Melt Spinning

Melt spinning was performed using a Fourne melt spinning machine (Fourne Polymertechnik GmbH, Germany) consisting of a 10 mm single screw extruder (rate 100 rpm), melt pump (rate 14 rpm) and multi strand filament die. The spinneret with 8 holes (diameter of 0.7 mm) was used. Spinning was performed at 130° C. The material was dried at ambient vacuum over night before processing. The melt spun fibers were collected and oriented using a drawing speed range of 0-200 m/min with and without an avivage agent.

Scanning Electron Microscopy (SEM)

Scanning electron microscopy analysis of the melt spun fiber was carried out using a field emission SEM (MERLIN FE-SEM, Carl Zeiss GmbH, Germany). 3 kV acceleration voltages were used. Prior to imaging, the fiber was and sputter coated (Leica EM ACE200, Germany) with a thin gold layer.

Tensile Testing of Fibers

Mechanical properties of melt spun fiber was analyzed using a Favimat+ testing system (Textechno, Germany) with a load cell of 210 cN and constant rate of crosshead speed of 20 mm/min. 20 replicate fibers were tested and the fibers were kept in standard conditions (23° C., 50% relative humidity) for one week before testing. Table 1 shows, as an example, properties of melt spun cellulose octanate fiber.

TABLE 1 drawing speed Avivage Draw ratio Thickness^(a) Linear density Tenacity Elongation (m/min) agent (DR) (μm) (dtex) (cN/dtex) (%) 0 no  0 760.0 ± 2.5  4177.2 ± 7.6   0.17 ± 0.03 223.0 ± 30.6  60 no 19 175.8 ± 1.4  213.3 ± 6.7  0.27 ± 0.03 6.4 ± 0.6 60 yes 15 204.6 ± 0.8  250.2 ± 37.6  0.19 ± 0.07 22.6 ± 7.3  80 no 38 123.3 ± 1.1  199.4 ± 23.5  0.20 ± 0.02 6.4 ± 0.4 80 yes 24 156.4 ± 0.7  182.4 ± 0.6  0.27 ± 0.03 20.5 ± 3.8  100 no 42 118.4 ± 0.2  118.6 ± 4.6  0.24 ± 0.03 12.7 ± 0.9  100 yes 37 124.7 ± 0.5  118.7 ± 3.3  0.29 ± 0.03 15.5 ± 2.8  120 no 53 104.1 ± 0.7  89.0 ± 4.3  0.27 ± 0.03 11.6 ± 2.5  120 yes 42 118.8 ± 0.3  97.5 ± 3.0  0.33 ± 0.08 13.8 ± 3.2  140 no 61 97.3 ± 0.3  75.8 ± 5.1  0.28 ± 0.02 9.6 ± 2.1 140 yes 52 105.5 ± 0.4  93.5 ± 4.9  0.31 ± 0.03 12.8 ± 3.3  160 no 73 88.9 ± 0.6  68.6 ± 1.8  0.30 ± 0.02 8.0 ± 0.9 160 yes 60 97.9 ± 0.6  65.7 ± 2.9  0.38 ± 0.06 10.7 ± 2.7  180 no 84 83.2 ± 0.4  64.8 ± 5.1  0.30 ± 0.02 7.5 ± 1.0 180 yes 80 85.0 ± 0.6  65.9 ± 0.6  0.36 ± 0.03 9.5 ± 2.5 200 no 97 77.2 ± 0.4  61.0 ± 5.8  0.34 ± 0.04 8.8 ± 2.4 200 yes 86 82.1 ± 0.7  63.2 ± 4.7  0.35 ± 0.02 9.8 ± 1.9 ^(a)according to SEM images nd. over the detection limit, not determined

CITATION LIST Patent Literature

-   WO 2016/193542 A1 -   JP 2005/248354 A

Non-Patent Literature

-   1. Chen B, Zhong L, Gu L (2010) Thermal properties and chemical     changes in blend melt spinning of cellulose acetate butyrate and a     novel cationic dyeable copolyester. J Appl Polym Sci 116:NA-NA. doi:     10.1002/app.30984 -   2. Hooshmand S, Aitomaki Y, Skrifvars M, et al (2014a) All-cellulose     nanocomposite fibers produced by melt spinning cellulose acetate     butyrate and cellulose nanocrystals. Cellulose 21:2665-2678. doi:     10.1007/s10570-014-0269-4 -   3. Hooshmand S, Cho S-W, Skrifvars M, et al (2014b) Melt spun     cellulose nanocomposite fibres: comparison of two dispersion     techniques. Plast Rubber Compos 43:15-24. doi:     10.1179/1743289813Y.0000000066 -   4. Wang X, Wang Y, Xia Y, et al (2018) Preparation, structure, and     properties of melt spun cellulose acetate butyrate fibers. Text Res     J 88:1491-1504. doi: 10.1177/0040517517703599 -   5. Willberg-Keyrilainen P, Talja R, Asikainen S, et al (2016) The     effect of cellulose molar mass on the properties of palmitate     esters. Carbohydr Polym 151:988-995. doi:     10.1016/j.carbpol.2016.06.048 -   6. Willberg-Keyrilainen P, Vartiainen J, Harlin A, Ropponen J     (2017a) The effect of side-chain length of cellulose fatty acid     esters on their thermal, barrier and mechanical properties.     Cellulose 24:505-517. doi: 10.1007/s10570-016-1165-x 

1. A melt spinning method for preparing continuous cellulose-based fibers, comprising at least the steps of: preparing a molar mass controlled cellulose ester having a side chain length between C6 and C18, a total degree of substitution from 0.7 to 3, and a molar mass distribution between 30 and 300 kDa from a cellulose raw material comprising cellulose, melt spinning the molar mass controlled cellulose ester to form melt spun fibers, and collecting the melt spun fibers, wherein the average molecular mass of the cellulose raw material is controlled via hydrolysis, excluding total hydrolysis.
 2. The method according to claim 1, wherein the cellulose raw material from a member selected from the group consisting of native softwood pulp, native hardwood pulp, annual plant pulp, softwood sulphite dissolving grade pulp, hardwood sulphite dissolving grade pulp, ozone treated hydrolyzed pulp, and enzyme treated pulp.
 3. The method according to claim 1, when the hydrolysis is controlled so that the average molecular mass of the cellulose is reduced at least 60% but not more than 85% from the molecular mass of the cellulose raw material, wherein, after the hydrolysis, the average molecular mass of the cellulose is in a range between 40 and 200 kDa.
 4. The method according to claim 1, wherein the cellulose raw material is hydrolyzed by enzymatic treatment, ozone treatment, hydrogen peroxide treatment, alkaline treatment or other chemical treatment.
 5. The method according to claim 1, wherein the molar mass controlled cellulose ester is prepared by homogenous esterification of the cellulose raw material by adding fatty acid chloride to the cellulose raw material using pyridine as catalyst at a reaction temperature of 80° C. and for a reaction time of 16 hours.
 6. The method according to claim 1, wherein the melt spinning is performed at a temperature between 120 and 150° C. using a melt spinning device having a single screw extruder, a melt pump, and a multi strand filament die.
 7. The method according to claim 1, wherein the melt spun fibers are collected using a drawing speed of 0 to 200 m/min.
 8. The method according to claim 1, wherein the molar mass controlled cellulose ester has a side chain length between C6 and C16.
 9. The method according to claim 1, wherein the molar mass controlled cellulose ester has a total degree of substitution between 0.9 and 2.0.
 10. A fully bio-based continuous melt spun molar mass controlled cellulose fiber having a thickness of at least 75 μm.
 11. The continuous melt spun molar mass controlled cellulose fiber according to claim 10, further comprising a tenacity of below 0.5 cN/dtex.
 12. The continuous melt spun molar mass controlled cellulose fiber according to claim 10, further an elongation of at least 5%.
 13. The continuous melt spun molar mass controlled cellulose fiber according to claim 10, wherein the fiber is manufactured according to the method of claim
 1. 14. A textile, fiber, filament, yarn, or cloth comprising a plurality of the continuous melt spun molar mass controlled cellulose fibers of claim
 10. 